1. Field of the Invention
The present invention relates to a rotary head type magnetic recording/playback apparatus which records signals while forming helical tracks on a magnetic tape with a rotary head. More particularly, this invention pertains to a digital VTR which records a digital video signal as well as a digital audio signal.
2. Description of the Related Art
Digital VTRs have an advantage that since they record or reproduce a video signal and an audio signal in the form of a digital signal, repetitive dubbing or editing will deteriorate neither the image quality nor the tone quality, thus ensuring high-quality signal recording and reproducing. These digital VTRs become popular first for industrial uses. There are two types of digital VTRs for industrial uses which have already been standardized and put into practical use: the D1 format VTR of component recording system and D2 format VTR of composite recording system.
FIG. 22 illustrates a track pattern on a magnetic tape in the D1 format digital VTR. Since it is difficult to record the whole amount of information of a digital video signal in one channel, the entire information is separated into four components which are then recorded in four channels in the D1 format of component recording type. As shown in FIG. 22 each helical track is divided into video recording regions 2001 and 2002 and an audio recording region 2003, with edit gaps 2004 and 2005 provided between these regions. In independently editing video and audio signals, the edit gaps 2004 and 2005 serve to enable or disable the erasing or recording while the associated head is scanning these areas.
FIG. 23 illustrates a track pattern on a magnetic tape in the D2 format digital VTR. In the D2 format of composite recording, the entire information of a digital video signal is separated into two components which are then recorded in two channels. Likewise, each helical track is divided into video recording region 2101 and audio recording regions 2102 and 2103, with edit gaps 2104 and 2105 provided therebetween, as shown in FIG. 23.
Though illustrated in neither FIG. 22 nor FIG. 23, each audio recording region is actually divided into smaller recording regions, with edit gaps also provided therebetween, so that independent editing is possible for individual audio channels. In FIGS. 22 and 23 three tracks formed along the tape, namely, a time code track, control track and cue audio track, are not shown.
In these conventional formats of digital VTRs, a digital audio signal is recorded on part of the helical track which also carries a video signal. This brings about an important advantage merit that the electromagnetic transformation section and some signal processors, which are associated with recording/playback of an audio signal, can be commonly used in recording/playback of a video signal. What can be shared include a mechanism, recording/playback head, recording/playback amplifier, modulation/demodulation circuit, waveform equalizing circuit, clock extracting circuit, synchronization pattern detecting circuit and part of an error correction coding/decoding circuit.
Most of the apparatuses associated with these formats are provided with the same number of audio advance playback heads as ordinary heads on the rotary drum. The advance playback heads are disposed at different heights with respect to the recording heads to reproduce signals of given times ahead in order to compensate for a time delay of an audio signal caused in the reproducing process and recording process. The audio data reproduced precedingly (read preceding or ahead) by the advance playback heads undergoes processing, such as mixing or filtering, and the processed audio data can be recorded again on the same (original) position on the tape.
A high definition television (HDTV) system which has over 1000 scan lines is receiving worldwide attention as a television system of the next generation. Although the detailed universal standards have not been established yet, development of this new television system is actively progressing in Japan. The HDTV has 1125 scan lines and uses a screen with a vertical-to-horizontal ratio of 9:16. The amount of information for the HDTV is more than five times that of the existing standard television system.
As a digital VTR for such an HDTV system having a huge amount of information, there exists a one-inch open reel type. This VTR is based on a one-inch type C VTR and divides a high definition signal into eight channels without compressing the information to record it digitally. An audio signal is digitally recorded on longitudinal tracks using a wide tape width. FIG. 24 shows a track pattern on a magnetic tape for one-inch open reel type high definition digital VTR; video recording regions 2201 to 2208 are helical tracks and an audio recording region 2209 is a longitudinal track (which actually consists of eight tracks). A time code track, control track and cue audio track, all formed along the tape, are not shown in FIG. 24.
Even for high definition digital VTRs, there is a growing demand for future appearance of a cassette type having better operability than the open reel type. It is therefore necessary to determine a new format for such a cassette type high definition digital VTRs. The format for the one-inch open reel type high definition VTRs cannot be used directly as the cassette type for the following reasons. Unlike in the open reel type, it is very difficult to increase the tape wrap angle close to 360.degree. for the cassette type. In addition, for the cassette type it is practical to set the tape width to 3/4 inch (about 19 mm) or narrower in order to reduce the mechanical load.
With regard to the system of recording an audio signal, with the use of a cassette with a 19-mm tape width, it becomes difficult to record multi-channel digital audio signals on longitudinal tracks due to the narrowed tape unlike in the one-inch high definition digital VTRs. In recording digital audio signals on longitudinal tracks, totally separate electromagnetic transformation sections and signal processors should be provided for video and audio signals while the aforementioned problems need to be addressed, and the adjustment and maintenance become more troublesome. Further, the edge portion of the tape where the longitudinal tracks are to be formed are easily damaged. In this respect, it is desirable to use a format to record an audio signal also on a helical track.
If digital audio signals are divided and recorded on the whole channels as performed in D1 and D2 formats, the following problems would arise.
(1) The amount of information of an audio signal per track becomes significantly smaller than that of a video signal, thus increasing the chance that audio data is impaired by a burst error. PA1 (2) Since edit gaps should be provided on the entire tracks for information editing, the redundancy of data increases inevitably. PA1 (3) The same number of advance playback heads for audio signals as the ordinary playback heads should be provided. In addition the increase in the number of the advance playback heads required results in an increase in the number of channels of the rotary transformer. For multi-channel recording VTRs of about eight channels, it is meaningless to further install the mentioned number of advance playback heads and rotary transformers only for editing of audio signals. PA1 input means for receiving a video signal and an audio signal; PA1 recording means for treating said inclined tracks as a plurality of track groups each including at least one first inclined track and a plurality of second inclined tracks, said recording means recording only a video signal on said second inclined tracks in each of said track groups, said second inclined tracks being used as video-only tracks, and recording a video signal and an audio signal in a mixed manner on said first inclined track used as a video/audio mixed track; PA1 reproducing means for reproducing said video signal and said audio signal from said inclined tracks in each of said track groups; and PA1 means for distributing the video signal to the first and second tracks of each of the track groups, in accordance with a predetermined distribution pattern which is determined in accordance with an integer ratio of the amount of data of an effective video signal per video-only track to the amount of data of an effective video signal per video/audio mixed track, the integer ratio being A:B and determined such that the number S of recorded video samples per line is divisible by P=A(N-K)+BK, where K video/audio mixed tracks are provided per N tracks, the effective video signals being video signals actually recorded on said video-only track and said video/audio mixed track. PA1 input means for receiving a video signal and an audio signal; PA1 recording means for treating said inclined tracks as a plurality of track groups each including at least one first inclined track and a plurality of second inclined tracks, said recording means recording only a video signal on said second inclined tracks in each of said track groups, said second inclined tracks being used as video-only tracks, and recording a video signal and an audio signal in a mixed manner on said first inclined track used as a video/audio mixed track; PA1 reproducing means for reproducing said video signal and said audio signal from said inclined tracks in each of said track groups; and PA1 means for distributing the luminance signal to the first and second tracks of each of the track groups, in accordance with a predetermined distribution pattern which is determined in accordance with a first integer ratio (K.sub..gamma.) of the amount of data of an effective luminance signal per video-only track to the amount of data of an effective luminance signal per video/audio mixed track, the integer ratio K.sub..gamma. =A.sub..gamma. /B.sub..gamma. being determined such that the number S.sub..gamma. of recorded luminance signal samples per line is divisible by P.sub..gamma. =A.sub..gamma. (N-K)+B.sub..gamma..K, where K video/audio mixed tracks are provided per N tracks, the effective luminance signals being luminance signals actually recorded on said video-only track and said video/audio mixed track and/or for distributing the color signals to the first and second tracks of each of the track groups, in accordance with a predetermined distribution pattern which is determined in accordance with a second integer ratio (K.sub.c) of the amount of data of an effective color signal per video-only track to the amount of data of an effective color signal per video/audio mixed track, the integer ratio K.sub.c =A.sub.c /B.sub.c being determined such that the number S.sub.c of recorded color signal samples per line is divisible by P.sub.c =A.sub.c (N-K)+B.sub.c.K, where K video/audio mixed tracks are provided per N tracks, the effective color signals being color signals actually recorded on said video-only track and said video/audio mixed track.
As described above, for the recording of audio signals on longitudinal tracks as performed in the conventional open reel type digital VTRs, totally separate electromagnetic transformation sections and signal processors are required for video and audio signals, and what is more, the adjustment and maintenance become more vexatious.
Since the technique of the conventional digital VTRs divides and records a digital audio signal on the entire channels, when it is applied to cassette type digital VTRs of a high definition television system, the amount of information of an audio signal per track is considerably reduced, causing audio data to be easily affected by a burst error. In addition, such application gives rise to increased redundancy due to the provision of edit gaps on the individual tracks, as well as a significant increase in the number of advance playback heads and the number of channels of the rotary transformer.